Under race bearing lubrication system for gas turbine engines

ABSTRACT

A bearing lubrication system for a gas turbine engine that has bearings supporting a rotor shaft comprises a housing for the engine that serves as a primary static structural support; a rotor shaft for mounting rotational components of the engine; at least two bearings for supporting the rotor shaft within the housing, each bearing comprising an inner race that couples to the rotor shaft comprising a plurality of inner race lubricant apertures that extend radially through the inner race that supply pressurised lubricant to selected regions within the bearing, an outer race that couples to a primary static structural support, a plurality of ball elements between the inner race and the outer race and a ball cage to maintain the relative radial spacing of the ball elements between each other within the inner race and the outer race; and a lubricant distribution system for delivering pressurised lubricant to the inner race apertures in each of the bearings.

FIELD OF THE INVENTION

The invention occurred with government support under Contract No.: F08635-03-C0002 awarded by the United States Air Force. The government has certain rights in the invention.

The invention relates to a lubrication system for gas turbine engines and more particularly to a lubrication system for ball bearing assemblies in a gas turbine engine.

BACKGROUND OF THE INVENTION

Miniature gas turbine or turbojet engines, typically of 150 lb-f thrust and smaller, are often useful for single-use airborne applications such as reconnaissance drones and other unmanned air and ground launched aeronautical vehicles. The use of such an engine greatly extends the range of such vehicles in comparison to the more conventional solid fuel rocket engine.

A miniature gas turbine engine must have a relatively inexpensive manufacturing cost coupled with a high degree of starting and operational reliability when launched from air or ground systems in order to be an economically feasible extended range expendable propulsion source for such applications. The high-speed ball bearings in a bearing system that support the rotating turbine machine are one type of component that greatly affects mechanical performance and reliability of a miniature gas turbine engine. Reliability and efficiency of the bearings in the bearing system are prime concerns for a successful expendable turbine engine. The most common cause of reduced reliability and efficiency of an expendable turbine engine bearing system is poor or inadequate lubrication of the bearings.

Although bearing systems for large reusable provide satisfactory reliability and efficiency, they employ a relatively complex closed circuit lubrication system that is relatively expensive to manufacture and difficult to maintain under the long term storage conditions needed for typical single use miniature gas turbine engines. Accordingly, it is desirable to achieve bearing lubrication with the reliability and efficiency of large turbine engines in an uncomplicated and inexpensive bearing lubrication system for a miniature gas turbine engine that assures a similar degree of operational efficiency and reliability.

SUMMARY OF THE INVENTION

The invention comprises an improved lubrication system for a miniature gas turbine that distributes lubricant to forward and aft bearings for supporting a rotor shaft in a miniature gas turbine engine by way of radial lubricant passages that pass through an inner ball race of each bearing.

Generally, the invention comprises a bearing lubrication system for a gas turbine engine that has bearings supporting a rotor shaft comprises a housing for the engine that serves as a primary static structural support; a rotor shaft for mounting rotational components of the engine; at least two bearings for supporting the rotor shaft within the housing, each bearing comprising an inner race that couples to the rotor shaft comprising a plurality of inner race lubricant apertures that extend radially through the inner race that supply pressurised lubricant to selected regions within the bearing, an outer race that couples to a primary static structural support, a plurality of ball elements between the inner race and the outer race and a ball cage to maintain the relative radial spacing of the ball elements between each other within the inner race and the outer race; and a lubricant distribution system for delivering pressurised lubricant to the inner race apertures in each of the bearings.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an expendable aeronautical vehicle that is suitable for incorporating at least one embodiment of the invention.

FIG. 2 is a cut-away side view of a miniature turbine engine for the expendable aeronautical vehicle shown in FIG. 1 that is suitable for incorporating at least one embodiment of the invention.

FIG. 3 is a detailed cut-away sectional side view of an inner race lubrication system for bearings in the miniature turbine engine shown in FIG. 2 according to a possible embodiment of the invention.

FIG. 4 is another detailed cut-away sectional side view of the lubrication system shown in FIG. 3.

FIG. 5 is a details cut-away sectional side view of a portion of the lubrication system shown in FIGS. 3 and 4 that lubricates a forward bearing one of the bearings.

FIG. 6 is a side view of a bearing assembly that may be suitable for use with the lubrication system shown in FIGS. 3 through 5.

FIG. 7 is a top view of a bearing assembly shown in FIG. 6.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 is a side view of an expendable aeronautical vehicle 2 that is suitable for incorporating at least one embodiment of the invention. The vehicle 2 comprises an airframe 4 with one or more aerodynamic surfaces 6. The vehicle 2 also comprises a propulsion engine 8, typically of the gas turbine or turbojet type. The engine 8 mounts within or to the vehicle 2. In FIG. 1, for purposes of illustration the engine 8 mounts within the vehicle 2, as shown in dashed line. An intake 10, shown in dashed line, supplies ambient air to the engine 8. An exhaust pipe 12, shown in dashed line, exhausts the thrust of the engine 8 to propel the vehicle 2.

FIG. 2 is a cut-away side view of a miniature turbine engine 8 for the expendable aeronautical vehicle shown in FIG. 1 that is suitable for incorporating the invention. The miniature gas turbine engine 8 generally comprises a housing 14, a rotor shaft 16 supported by a forward bearing 18 and an aft bearing 20, a generally annular combustion chamber 22 and an exhaust pipe 24. The forward bearing 18 and the aft bearing 20 allow the rotor shaft 16 to rotate about a longitudinal axis X. The forward bearing 19 and the aft bearing 20 are both of the ball bearing type.

A multi-bladed compressor wheel 26 mounted on the rotor shaft 16 faces forward toward an intake 28 and a multi-bladed turbine wheel 30 mounted on the rotor shaft 16 faces rearward toward the exhaust pipe 24. The forward bearing 18 and the aft bearing 20 support the rotor shaft 16 to extend it at least partially into a forward cover 32. The forward cover 32 is preferably the forward-most portion of the engine 8 and defines an aerodynamically contoured shape. The intake 28 generally surrounds the forward cover 32 to facilitate airflow.

A permanent magnet generator (PMG) 34 preferably mounts on the rotor shaft 16 between the forward bearing 18 and the aft bearing 20 to generate electrical power for the engine 8 and other accessories. The PMG 34 comprises a stator 36 that mounts to the housing 14 by way of a housing inner support 38 and a rotor 40 mounted on the rotor shaft 16. An electrical power line 42 transfers electrical power from the PMG 34 to an electrical power system 44.

A fuel pump 46 to pump fuel from a fuel source 48 by way of a fuel source line 50 pumps fuel to the annular combustion chamber 22 by way of a pump supply line 52 through a fuel manifold 54. The electrical power system 44 preferably drives the fuel pump 46, although alternatively the turbine wheel 30 could drive the fuel pump 46 by way of a suitable transmission (not shown) coupled to the rotor shaft 16. The fuel burns at high temperatures within the combustor chamber 22 to generate expanding exhaust gases that flow through a turbine nozzle 56, the turbine wheel 30 and the exhaust pipe 24 thereby driving the turbine wheel 30 and generating a high velocity thrust out of the exhaust pipe 24.

A fastener 58, such as a threaded rotor nut or bolt, may conveniently couple to a mating end portion 60 of the rotor shaft 16, such as a threaded stud or aperture, to retain the rotor shaft 16 within the forward bearing 18 and the aft bearing 20. The housing inner support 38 conveniently mounts the forward bearing 18 and the aft bearing 20 to the housing 14.

The housing 14 provides the primary static structural support for rotation of the rotor shaft 16 and the hereinbefore-described rotational components mounted on it. The fastener 58 extends at least partially within he forward cover 32. The forward cover 32 mounts to the housing 14. Removal of the forward cover 32 facilitates assembly and disassembly by providing access to the fastener 58.

The housing 14 includes a lubrication line 62 supplied by a lubrication source that supplies suitable bearing lubricant, such as fuel, oil or a mixture thereof to the bearings 18 and 20. The lubrication source may conveniently be the fuel source 48, in which case the lubrication line 62 may couple to the fuel source line 50. The lubrication line 62 may conveniently supply a plurality radial lubricant passages (not shown) arranged about each of the bearings 18 and 20.

In any case, the lubricant delivery preferably sprays lubricant onto the bearings 18 and 20. Such lubrication delivery still further improves reliable operation. Furthermore, the cooling airflow that passes through the forward cover 32 propagates lubricant that collects aft of the forward bearing 18 toward the aft bearing 20 and into the combustion chamber 22. Using a fuel or a fuel oil mixture as the lubricant maintains engine efficiency, since the lubricant ultimately propagates into the combustion system 22 for combustion and thrust generation.

FIG. 3 is a detailed cut-away sectional side view of an inner race lubrication system 64 for the bearings 18 and 20 according to a possible embodiment of the invention. FIG. 4 is another detailed cut-away sectional side view of the lubrication system shown in FIG. 3. FIG. 5 is a details cut-away sectional side view of a portion of the lubrication system 64 shown in FIGS. 3 and 4 that lubricates the forward bearing 18. FIG. 6 is a side view of a bearing assembly construction for the bearings 18 and 20 that may be suitable for use with the lubrication system shown in FIGS. 3 through 5. FIG. 7 is a top view of the bearing assembly construction for the bearings 18 and 20 shown in FIG. 6.

Referring to FIGS. 3 through 5 together, the lubrication system 64 comprises a forward bearing lubricant path 66 and an aft bearing lubricant path 68. The forward bearing lubricant path 66 couples to the lubrication line 62 by way of a forward bearing lubricant path port 70. Lubricant under pressure from the lubrication line 62 passes through the forward bearing lubricant path 66 into a forward bearing lubricant galley 72.

Referring to FIGS. 6 and 7 together, each bearing 18 and 20 has a plurality of ball elements 74 arranged radially between an inner race 76 and an outer race 78. A ball cage 80 comprises a plurality of cage apertures 82 arranged around its periphery that each retain a respective ball element 74 and serve to maintain the relative radial spacing of the ball elements 74 between each other within the inner race 76 and the outer race 78.

Each bearing 18 and 20 has at least one radial row of inner race apertures 84 that pass radially through the inner race 76. Referring to FIGS. 3 through 6 together, lubricant under pressure from the forward bearing lubricant galley 72 passes through each of two radial rows of the inner race apertures 84 in the inner race 76 of the forward bearing 18 to direct lubrication to selected regions within the forward bearing 18.

At the same time, the aft bearing lubricant path 66 couples to the lubrication line 62 by way of an aft bearing lubricant path port 86. Lubricant under pressure from the lubrication line 62 passes through the aft bearing lubricant path port 66 into a rotor shaft lubricant channel 88 that extends axially within the rotor shaft 16. Lubricant under pressure from the rotor shaft lubricant channel 88 then passes through a plurality of lubricant supply channels 90 that extend radially from the rotor shaft lubricant channel 88 and through at least one radial row of mating inner race apertures 84 in the inner race 76 of the aft bearing 20 to direct lubrication to selected regions within the aft bearing 20.

Referring to FIGS. 3 and 4, cooling airflow passes through an air inlet 92 that preferably comprises an air filter 94 that filters the cooling airflow. The filtered cooling airflow flows over and through the forward bearing 18 along the rotor shaft 16, over and through the PMG 34, then over and through the aft bearing 20 to provide significant thermal management of these components.

Relative positional terms as hereinbefore described, such as “forward”, “aft”, “upper”, “lower”, “above”, “below”, and the like are with reference to the normal operational attitude and should not be considered otherwise limiting.

The described embodiment of the invention is only an illustrative implementation of the invention wherein changes and substitutions of the various parts and arrangement thereof are within the scope of the invention as set forth in the attached claims. 

1. A ball bearing assembly for supporting a rotor shaft in a gas turbine engine, comprising: an inner race that couples to the rotor shaft comprising a plurality of inner race lubricant apertures that extend radially through the inner race that supply pressurised lubricant to selected regions within the bearing; an outer race that couples to a primary static structural support; a plurality of ball elements between the inner race and the outer race; and a ball cage to maintain the relative radial spacing of the ball elements between each other within the inner race and the outer race.
 2. The ball bearing assembly of claim 1, wherein the inner race lubricant apertures form at least one radial row around the inner race.
 3. The ball bearing assembly of claim 2, wherein the inner race lubricant apertures form two radial rows around the inner race.
 4. A bearing lubrication system for a gas turbine engine that has bearings supporting a rotor shaft, comprising: a housing for the engine that serves as a primary static structural support; a rotor shaft for mounting rotational components of the engine; at least two bearings for supporting the rotor shaft within the housing, each bearing comprising an inner race that couples to the rotor shaft comprising a plurality of inner race lubricant apertures that extend radially through the inner race that supply pressurised lubricant to selected regions within the bearing, an outer race that couples to a primary static structural support, a plurality of ball elements between the inner race and the outer race and a ball cage to maintain the relative radial spacing of the ball elements between each other within the inner race and the outer race; and a lubricant distribution system for delivering pressurised lubricant to the inner race apertures in each of the bearings.
 5. The bearing lubrication system of claim 4, wherein the lubricant comprises fuel for the engine.
 6. The bearing lubrication system of claim 4, wherein the lubricant comprises oil.
 7. The bearing lubrication system of claim 4, wherein the lubricant comprises a mixture of fuel for the engine and oil.
 8. The bearing lubrication system of claim 4, wherein the lubricant distribution system comprises a lubricant source that supplies the lubricant.
 9. The bearing lubrication system of claim 8, wherein the lubricant distribution system further comprises a lubricant pump for pressurising the lubricant.
 10. The bearing lubrication system of claim 9, wherein the lubricant distribution system further comprises a pressurised lubricant galley for supplying lubricant to a forward one of the bearings.
 11. The bearing lubrication system of claim 9, wherein the lubricant distribution system further comprises a pressurised rotor shaft lubricant channel for supplying lubricant to at least one aft bearing.
 12. The bearing lubrication system of claim 4, wherein airflow through the engine propagates lubricant from a forward one of the bearings to at least one aft bearing and into a combustion chamber for the engine.
 13. A gas turbine engine comprising: a housing for the engine that serves as a primary static structural support; a rotor shaft; a compressor wheel mounted on the rotor shaft for compressing air; a combustion chamber for combusting the compressed air with fuel to generate expanding exhaust gas; a turbine wheel mounted on the rotor shaft driven by the expanding exhaust gas; at least two bearings for supporting the rotor shaft within the housing, each bearing comprising an inner race that couples to the rotor shaft comprising a plurality of inner race lubricant apertures that extend radially through the inner race that supply pressurised lubricant to selected regions within the bearing, an outer race that couples to a primary static structural support, a plurality of ball elements between the inner race and the outer race and a ball cage to maintain the relative radial spacing of the ball elements between each other within the inner race and the outer race; and a lubricant distribution system for delivering pressurised lubricant to the inner race apertures in each of the bearings.
 14. The engine of claim 13, wherein the lubricant comprises fuel for the engine.
 15. The bearing lubrication system of claim 13, wherein the lubricant comprises oil.
 16. The engine of claim 13, wherein the lubricant comprises a mixture of fuel for the engine and oil.
 17. The engine of claim 13, wherein the lubricant distribution system comprises a lubricant source that supplies the lubricant.
 18. The engine of claim 17, wherein the lubricant distribution system further comprises a lubricant pump for pressurising the lubricant.
 19. The engine of claim 18, wherein the lubricant distribution system further comprises a pressurised lubricant galley for supplying lubricant to a forward one of the bearings.
 20. The engine of claim 18, wherein the lubricant distribution system further comprises a pressurised rotor shaft lubricant channel for supplying lubricant to at least one aft bearing.
 21. The bearing lubrication system of claim 13, wherein airflow through the engine propagates lubricant from a forward one of the bearings to at least one aft bearing and into a combustion chamber for the engine. 